DESCRIPTION (Applicant's Abstract): The pneumococcus remains the cause of meningitis with the greatest morbidity and mortality in children and older adults. This pattern persists despite the use of antibiotics of exceptionally rapid bactericidal activity. Over the past 15 years of this proposal, we have sought to understand the biochemical basis of the inflammatory response to pneumococci in the subarachnoid space and to determine how pneumococci traffic through cerebral microvessels. In the past 5 years, we established that the pneumococcal cell wall is a library of inflammatory components that signals through LBP and TLR2 and causes two kinds of apoptosis of neurons. We found that pneumococci bind via choline binding protein A to the polymeric Ig receptor of epithelia and the PAF receptor of endothelia to invade cells. Finally, we determined the unusual NMR structure of the adhesin CbpA. Broadly, the current proposal seeks to determine the molecular details of the mechanism of pneumococcal invasion across the blood brain barrier and to show how cell wall components directly inhibit neuronal regeneration. Over half of the current survivors of pneumococcal meningitis still have major permanent sequelae. Understanding these processes will help design of agents to specifically attenuate neuronal losses. We propose to apply our expertise in the identification and characterization of pneumococcal surface components to mapping the process of transcytosis across the blood brain barrier. Having solved the structure activity relationship of CbpA, we will turn to its partner CbpG, a serine protease that potentiates invasion by CbpA at the BBB. Secondly, we will characterize the process of pneumococcal translocation in terms of the intracellular vesicular machinery and the signaling process for translocation via PAF receptor. We will visualize translocation in vivo using a cranial window and compare knock out mice for defects in bacterial transport across the blood brain barrier. Finally, we will investigate a new hypothesis that pneumococcal cell wall translocates to the nucleus, binds transcription factors, and directly inhibits neuroregeneration.